Internal combustion engine design has been continuously modified in numerous different ways ever since the introduction thereof. The motivation for these design changes has historically stemmed from the desire to increase the engine efficiency. Moreover, most attempts are made to improve efficiency reliability and/or increase the power output from the internal combustion engine. One known variety of improvements includes the modification of a conventional engine cycle with a four stroke cycle that is completed during a single revolution of an engine crankshaft. A four stroke engine cycle is defined as including an intake stroke, a compression stroke, a power expansion stroke and an exhaust stroke. To complete each of these aforementioned strokes, at least one piston is moved twice in a reciprocating manner within a cylinder bore from a top dead center position (hereinafter abbreviated TDC) to a bottom dead center position (hereinafter abbreviated BDC). Typically, four strokes occur over two revolutions of the engine crankshaft wherein a first revolution defines the compression and expansion strokes and the second revolution defines the exhaust and intake strokes. The crankshaft is rotatably mounted to an engine block and is provided with an offset crank portion that is rotatably connected to a connecting rod, which is further rotatably connected to a wristpin affixed with the piston. By this, the reciprocating piston motion is translated to rotary motion, wherein only a single power stroke is completed for every two revolutions.
In order to complete a four stroke cycle within a single crank revolution, it becomes necessary to conduct one power stroke for each crankshaft revolution. In order to accomplish this the piston must travel through two reciprocating motions during the single revolution of the crankshaft. The above mentioned rotatable connection, included in a conventional four stroke cycle, between a connecting rod and the crankshaft cannot facilitate this type of motion.
Attempts at making a crankshaft, that can facilitate two reciprocations of the piston during one revolution, have been basically focused on two areas. One of these areas has been to use a rotatable camshaft as the crankshaft, wherein the camshaft includes dual cam lobes, and each lobe corresponds to one piston reciprocation equal in duration to the second piston reciprocation. Known devices include an element extending from the piston to ride against the cam surface of the camshaft, wherein the element, such as a roller, follows along each of the cam lobes of the camshaft. Therefore, the power stroke of the piston and attached element imparts the rotational drive force to the camshaft during one inward piston stroke of every camshaft rotation.
The use of roller elements provided on extensions from the piston and a cam lobed crankshaft is not limited to internal combustion engines of the variety above described. Such a cam operated crankshaft is of use in a conventional type four stroke cycle wherein one revolution translates into one reciprocal motion of the piston. Examples of cam driven shafts are disclosed in U.S. Pat. No. 2,004,498 to Dasset and No. 3,025,840 to Casini.
The second area of focus of four stroke single revolution engines, includes devices utilizing linkage systems which allow the piston to be reciprocated twice during a single revolution of the driven output shaft. In order for these linkage systems to work, it is necessary to include a drive link extending from the piston, with the distal end thereof moved from side to side across the longitudinal axis of the piston and cylinder. Such movement provides two piston reciprocations to a single revolution of a crankshaft, wherein the crankshaft is attached by link to the distal end of the drive link. These devices are disadvantageous in that they require a relatively large amount of moving parts and more importantly require a large operating area. Such devices are impractical for commercial use because they increase the size and weight of the engine as well as the costs thereof.
Internal combustion engines are also known with variable stroke mechanisms for increasing the power output from the engine and thus increasing the efficiency thereof. An example of a variable stroke engine is disclosed by Nelson U.S. Pat. No. 4,517,931. This patent illustrates an increased power output by having a longer power stroke and exhaust stroke than the intake stroke and compression stroke. However, this mechanism requires a complex trunion assembly and a control shaft connected by a control link to thereby variably permit a longer downward stroke for the power stroke.